Weather map showing an occluded front
Click on image for full size
Windows to the Universe image by Lisa Gardiner
Sometimes a cold front follows right behind a warm front. Because cold fronts move faster, the cold front can run into the warm front. This is called an occluded front.
At an occluded front, the cold air from the cold front meets the cool air that was in front of the warm front. The warm air rises. Occluded fronts usually form around low pressure areas.
There is often rain or snow along the front from cumulonimbus or nimbostratus clouds. Wind changes direction as the front passes and the temperature changes too. After the front passes, the sky is usually clearer.
On a weather map, like the one on the left, an occluded front looks like a purple line with half triangles and half semicircles pointing in the direction that the front is moving. At one end there is a low pressure area (the ‘L’). At the other end, the occluded front connects to cold and warm fronts.
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